Re: Commutative property of arithmetic operations with NA and NaN

[Francesco Potortì]

>octave:1> NaN*NA
>ans = NA
>octave:2> NA*NaN
>ans = NaN
...
>octave:5> NaN + NA
>ans = NA
>octave:6> NA + NaN
>ans = NaN

Waiting for more knowledgeable opinions, here is what I remember) caveat
emptor).

NaN is defined by IEEE standards.  It has not a single binary
representations, so two NaN values may legally have different underlying
binary representations.

NA is a particular NaN representation which is used in the R language,
from which Octave copies the semantic meaning.  It is commonly used in
data series to indicate a missing values (Not Available).

Examples of usage are the NaN and TSA packages, which however do not
require NA to be used, but are happy with NaN:
http://pub.ist.ac.at/~schloegl/matlab/NaN/

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